CN112946544B - Double-resonance detection device for nuclear magnetic resonance radio frequency coil - Google Patents
Double-resonance detection device for nuclear magnetic resonance radio frequency coil Download PDFInfo
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- CN112946544B CN112946544B CN202110137890.0A CN202110137890A CN112946544B CN 112946544 B CN112946544 B CN 112946544B CN 202110137890 A CN202110137890 A CN 202110137890A CN 112946544 B CN112946544 B CN 112946544B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
- G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
- G01R33/34007—Manufacture of RF coils, e.g. using printed circuit board technology; additional hardware for providing mechanical support to the RF coil assembly or to part thereof, e.g. a support for moving the coil assembly relative to the remainder of the MR system
Abstract
The invention discloses a nuclear magnetic resonance radio frequency coil double resonance detection device, which comprises an input port, an input matching capacitor module, a balance capacitor module, a resonance inductance module, an output port and an output matching capacitor module.
Description
Technical Field
The invention relates to the technical field of nuclear magnetic resonance instruments, in particular to a nuclear magnetic resonance radio frequency coil double-resonance detection device which is suitable for a nuclear magnetic resonance spectrometer or a nuclear magnetic resonance imager and is used for realizing double-resonance experimental detection of nuclides with two resonance frequencies close to each other.
Background
The nuclear magnetic resonance radio frequency coil is a key component for exciting and collecting nuclear magnetic resonance signals, and the resonance point of the radio frequency coil can be tuned to the resonance frequency of different nuclides by adjusting the capacitance value of an adjustable capacitor connected with the coil, so that the aim of observing the magnetic resonance signals of different nuclides is fulfilled. In the nuclear magnetic resonance detection technology, signals of two nuclides with different resonance frequencies need to be excited and received simultaneously, the existing nuclear magnetic resonance radio frequency coil is mainly realized by a double-coil method and a double-resonance method, the double-coil method is to design an independent magnetic resonance coil for each nuclide, and the two coils are nested inside and outside and then are used for detecting the signals of the two nuclides. The double resonance method is to design a special resonance circuit, so that two resonance points are generated by a single coil and then two nuclide signals are detected.
However, no matter the rf coil designed based on the dual-coil method or the dual-resonance method, the current commercial mr rf coil cannot realize dual-resonance detection of a nuclear species with a close resonance frequency (usually, a dual-channel resonance frequency difference value is required to be greater than 20%), because the current scheme of the dual-coil type nmr rf coil adopts a mode of separately designing high and low frequency bands, generally, the nuclear species with a higher resonance frequency (e.g. 1H, 19F) is used as one detection channel, the nuclear species with a lower resonance frequency (e.g. 13C, 23Na) is used as another detection channel, when performing dual-resonance experimental detection, only one high frequency core and one low frequency core can be detected at the same time, and signals of the two high frequency cores with close frequencies or the two low frequency cores with close frequencies cannot be observed at the same time. However, the current dual-resonance type rf coil is designed only for the commonly used nuclear species with fixed frequency, such as the dual-resonance coil with 13C and 15N nuclei or the dual-resonance coil with 31P and 23Na nuclei, and if the dual-resonance detection needs to be performed on the other two nuclear species, the dual-resonance excitation or detection of the nuclear species with a frequency close to the frequency cannot be realized due to the limited adjustable range.
With the continuous development of nuclear magnetic resonance technology and the expansion of application range, researchers have made urgent demands for dual resonance experiments for simultaneously detecting a resonance frequency close to a nuclear species, such as 129Xe-27Al dual resonance experiments required in the study of a molecular sieve pore structure and a diffusion effect, 31P-7Li dual resonance experiments related to lithium phosphate batteries, dual resonance experiments for simultaneously irradiating two NMR observable isotopes of metallic tin, i.e., 117Sn and 119Sn, and the like. However, the above-mentioned dual resonance experiment with a frequency close to nuclear cannot be realized by commercial magnetic resonance coils at present, and no document reports on dual resonance rf coils and devices for realizing a frequency close to nuclear species are found, which greatly hinders the research of related NMR spectroscopy in related fields, and therefore, it is very important to design a dual resonance rf coil or device for realizing a frequency close to nuclear species.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides the nuclear magnetic resonance radio frequency coil double-resonance detection device which can realize double-resonance experimental detection of two nuclides with close resonance frequencies under the condition of not changing the structure of the conventional single nuclide radio frequency coil. The above object of the present invention is achieved by the following technical solutions:
the utility model provides a two resonance detection device of nuclear magnetic resonance radio frequency coil, includes input port and output port, input port match electric capacity module one end with balanced capacitance module one end and input respectively and be connected, the input matches the electric capacity module other end and is connected with electrical ground, the balanced capacitance module other end is connected with resonance inductance module one end, the resonance inductance module other end matches electric capacity module one end with output respectively and output port is connected, the output matches the electric capacity module other end and is connected with electrical ground.
Compared with the prior art, the invention has the following advantages:
1. the device is connected with the existing single-core radio frequency coil, so that double resonance experiment detection of two nuclides with resonance frequencies close to each other can be realized;
2. the device can be used by externally connecting the device to the existing single resonance magnetic resonance coil without changing the circuit structure and the mechanical structure of the existing single resonance magnetic resonance coil, and has strong flexibility and compatibility;
3. the device can design matching capacitors and balance capacitors with different capacitance values and different numbers according to different experimental requirements, realizes double resonance experimental detection of resonance frequency close to nuclide in various frequency bands, and has wide frequency coverage range, expansion range and the like.
Drawings
FIG. 1 is a schematic diagram of the principles of the present invention;
FIG. 2 is an equivalent schematic of the present invention; wherein (a) is an equivalent schematic diagram of the invention after being connected with a single resonance magnetic resonance coil; (b) the invention is an equivalent schematic diagram under a first resonance mode after being connected with a single resonance magnetic resonance coil; (c) is an equivalent schematic diagram under a second resonance mode after the single-resonance magnetic resonance coil is connected with the invention;
FIG. 3 is a schematic view of an embodiment of the present invention;
FIG. 4 is a graph showing the effect of the embodiment of the present invention, i.e., on dehydrated Sn/Beta molecular sieves 1 H-{ 117 Sn/ 119 Sn } S-REDOR experiment result chart.
Detailed Description
The present invention will be described in further detail with reference to examples for the purpose of facilitating understanding and practice of the invention by those of ordinary skill in the art, and it is to be understood that the present invention has been described in the illustrative embodiments and is not to be construed as limited thereto.
Example 1
As shown in FIG. 1, a dual resonance detection apparatus for nuclear magnetic resonance RF coil comprises an input port 1, an input matching capacitor module 2, a balance capacitor module 3, a resonance inductor module 4, an output matching capacitor module 5 and an output port 6,
the input port 1 is connected with one end of the balance capacitor module 3 and one end of the input matching capacitor module 2 respectively, the other end of the input matching capacitor module 2 is connected with the electrical ground, the other end of the balance capacitor module 3 is connected with one end of the resonance inductor module 4, the other end of the resonance inductor module 4 is connected with one end of the output matching capacitor module 5 and the output port 6 respectively, and the other end of the output matching capacitor module 5 is connected with the electrical ground.
The input port 1 is used for connecting a radio frequency signal output by the radio frequency power amplifier and outputting the received radio frequency signal to the input matching capacitor module 2 and the balance capacitor module 3, and the type of the input port 1 can adopt N-KFD 6.
The input matching capacitor module 2 is used for performing characteristic impedance matching on the radio frequency signal introduced by the input port 1 to ensure that the reflection power of the radio frequency signal of the input port 1 is minimum, the radio frequency signal is output to the balance capacitor module 3 after matching, and the input matching capacitor module 2 can adopt AT40HV in model.
And the balance capacitor module 3 is used for adjusting the reflected power AT the two resonance frequencies, the adjusted radio frequency signal is output to the resonance inductance module 4, and the model of the balance capacitor module 3 can adopt AT40 HV.
The resonance inductance module 4 is used for adjusting the radio frequency signal output by the balance capacitance module 3, so that the single resonance magnetic resonance coil circuit connected with the output port 6 is converted into a double resonance magnetic resonance coil circuit, the radio frequency signal output by the balance capacitance module 3 is adjusted and output to the output matching capacitance module 5 and the output port 6, and the model of the resonance inductance module 4 can adopt SER2211-822 MED.
The output matching capacitor module 5 is configured to perform characteristic impedance matching on the radio frequency signal AT the output port 6, so as to ensure that the reflected power of the radio frequency signal AT the output port 6 is minimum, the matched radio frequency signal is output to the output port 6, and the model of the output matching capacitor module 5 may be AT40 HV.
And the output port 6 is used for connecting the radio-frequency signal output by the device to the input port of the single-resonance radio-frequency coil, and the type of the output port 6 can adopt N-JF-1.
The output end of the input port 1 is connected with an electrical ground through the input matching capacitor module 3, the output end of the input port 1 is connected with one end of the balance capacitor module 3, the other end of the balance capacitor module 3 is connected with one end of the resonance inductor module 4, and the other end of the resonance inductor module 4 is connected with the electrical ground through the output matching capacitor module 5 and is connected with the input end of the output port 6.
The input matching capacitor module 2 is at least one capacitor, the balance capacitor module 3 is at least one capacitor, the resonance inductor module 4 is at least one inductor, and the output matching capacitor module 5 is at least one capacitor.
The principle schematic diagram of the invention is shown in fig. 1, and the device is arranged between the output end of a radio frequency power amplifier and the input end of the existing single resonance radio frequency coil and is respectively connected with the output end of the radio frequency power amplifier and the input end of the single resonance radio frequency coil through an input port 1 and an output port 6. After the device is connected, two resonance frequencies can be observed on a reflected power test chart, wherein one resonance frequency is the frequency of the original single resonance radio frequency coil, the other resonance frequency is a new resonance frequency near the resonance frequency of the single resonance radio frequency coil, the reflected power at the two resonance frequencies can be adjusted by adjusting the adjustable capacitance value of the input matching capacitor module 2 and the adjustable capacitance value of the output matching capacitor module 5, and meanwhile, the reflected power at the two resonance frequencies can be adjusted by adjusting the adjustable capacitance value of the balance capacitor module 3. The resonant inductor module 4 functions to extend the existing single-nuclei resonance frequency to two frequencies close to the resonance frequency of the nuclear species. In addition, in order to realize double resonance experiment detection in a larger range, the input matching capacitor module 2, the balance capacitor module 3 and the output matching capacitor module 5 of the device can be respectively composed of a single or a plurality of adjustable capacitors or fixed capacitors, the adjustable capacitors or the fixed capacitors with different sizes and different quantities can be flexibly accessed according to the requirements of different resonance frequencies, the double resonance experiment detection in a wider frequency range can be met, and the device has strong expandability and compatibility. Based on this device, can reform transform into the double resonance magnetic resonance coil of frequency approximate nuclide with current single resonance magnetic resonance coil to solve current commercial magnetic resonance coil and can't realize the double resonance excitation or the detection problem of frequency approximate nuclide.
The following explains in principle how the apparatus transforms a single resonance magnetic resonance coil into a dual resonance magnetic resonance coil with a frequency close to that of a nuclear species:
an equivalent circuit diagram of the device and the single-resonance magnetic resonance coil after being connected in series is shown in fig. 2, wherein a third equivalent capacitor C3, a second equivalent capacitor C2 and a second equivalent inductor L2 form a basic form of the single-resonance magnetic resonance coil, the first equivalent inductor L1 is an equivalent circuit formed by connecting the balance capacitor module 3 and the resonance inductor module 4 in series and can be regarded as an adjustable equivalent inductor L1, and the equivalent condition is that the inductive reactance of the resonance inductor module 4 in series is greater than the capacitive reactance of the balance capacitor module 3 in series and the equivalent circuit diagram is realized by calculating the equivalent impedance. Since the capacitance value of the balance capacitance module 3 is small, the following equivalence can be made. Is derived by formula: assuming that the size of the series resonant inductor module 4 is L and the size of the series balance capacitor module 3 is C, the series impedance is
The equivalent inductance is assumed to be L1
According to the formula, the equivalent inductance can be calculated
ω is the angular frequency of the rf signal input from the input port 1, and when the inductive reactance of the series resonant inductor module 4 is greater than the capacitive reactance of the series balanced capacitor module 3, it is an inductive element, so it can be equivalent to an adjustable inductor. In this way, since the tunable inductor is difficult to be implemented in practical applications, the inductance value is indirectly changed by serially connecting the small-capacity tunable capacitor, so as to implement the function of the tunable inductor, the first equivalent capacitor C1 is the equivalent capacitor of the output matching capacitor module 5, and the fourth equivalent capacitor C4 is the equivalent capacitor of the input matching capacitor module 2.
When the output port 6 and the single-resonance magnetic resonance coil are connected in series, resonance splitting is generated, the two resonance modes work in two resonance modes, two resonance modes generate reverse phase voltage and in-phase voltage at two ends of a third equivalent capacitor C3, circuits of the two resonance modes are equivalent to a circuit shown in a figure 2(b) and a circuit shown in a figure 2(C) respectively, wherein a third equivalent inductor L3 is an equivalent circuit formed by connecting a first equivalent inductor L1 and a fourth equivalent capacitor C4 in series, the inductive reactance of the third equivalent inductor L3 is greater than that of the fourth equivalent capacitor C4, and the circuit is also regarded as an adjustable equivalent inductor,
the resonance conditions are L3 ═ L2, C1 ═ C2, and when the circuit operates in the first resonance mode, the voltage across the third equivalent capacitor C3 is reversed, so the midpoint potential of the third equivalent capacitor C3 is zero, i.e. the circuit can be equivalent to be in the first resonance modeCircuit diagram 2(b) after the parallel connection of two capacitors with capacitance value of 2C3 (capacitance value of 2 times C3). When the circuit works in the second resonant mode, the voltages at the two ends of the third equivalent capacitor C3 are in phase, which is equivalent to the third equivalent capacitor C3 being open-circuited, i.e. the circuit is equivalent to two separate resonant circuits as shown in fig. 2 (C). The two resonance frequencies respectively correspond to:
therefore, the device and the single resonance magnetic resonance coil are connected to generate omega 1 And omega 2 Two resonance frequencies forming a dual resonance magnetic resonance coil with a frequency close to the nuclear species.
The series connection of the balance capacitor module 3 and the resonance inductor module 4 is equivalent to an adjustable first equivalent inductor L1, and then the series connection of the first equivalent inductor L1 and the input matching capacitor module 2 is equivalent to an adjustable inductor L3, and after the two equivalent circuits are completed, the equivalent circuits in fig. 2(b) and fig. 2(c) are formed. When the equivalent circuit is used for analyzing the resonance mode, the input port and the output port do not influence the resonance mode of the circuit.
In fig. 2(b), 2C3 is the capacitance of the third equivalent capacitor C3 with capacitance value 2 times, and when the circuit operates in the first resonance mode, the voltage across the third equivalent capacitor C3 is reversed, so the midpoint potential of the third equivalent capacitor C3 is zero, i.e. the circuit is equivalent to the circuit of fig. 2(b) after two capacitors with capacitance value 2C3 are connected in parallel. When the circuit works in the second resonant mode, the voltages at the two ends of the third equivalent capacitor C3 are in phase, which is equivalent to the third equivalent capacitor C3 being open-circuited, i.e. the circuit is equivalent to two separate resonant circuits as shown in fig. 2 (C).
FIG. 3 shows an example of the experimental design of the double resonance detection apparatus 1H- {117Sn/119Sn } S-REDOR based on the invention. In the presence of metallic tin in natural abundance, two NMR observable isotopes 117Sn (7.68%) and 119Sn (8.59%) exist, the Lamor resonance frequency is 178.2MHz and 186.6MHz respectively under the field strength of 11.7T, and a conventional commercial NMR probe cannot simultaneously irradiate the two isotopes to carry out a double resonance experiment. Therefore, the highest efficiency of the difference spectrum before and after Sn irradiation in the S-REDOR experiment of single irradiation of 1H-119Sn or 1H-117Sn is about 7-8% (related to the natural abundance of the corresponding isotope). In a 1H- {117Sn/119Sn } S-REDOR experiment designed by the double-resonance detection device, 117Sn and 119Sn nuclides in an Sn/Beta molecular sieve sample can be subjected to double-resonance irradiation at the same time, and the difference spectrum signal of 1H before and after irradiation is improved to 15 percent, as shown in figure 4, the experiment efficiency is improved by nearly one time.
The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.
Claims (1)
1. A nuclear magnetic resonance radio frequency coil double resonance detection device comprises an input port (1) and an output port (6), and is characterized in that the input port (1) is respectively connected with one end of a balance capacitor module (3) and one end of an input matching capacitor module (2), the other end of the input matching capacitor module (2) is electrically connected with the ground, the other end of the balance capacitor module (3) is connected with one end of a resonance inductor module (4), the other end of the resonance inductor module (4) is respectively connected with one end of an output matching capacitor module (5) and the output port (6), the other end of the output matching capacitor module (5) is electrically connected with the ground, the input port (1) and the output port (6) are respectively connected with the output end of a radio frequency power amplifier and the input end of a single resonance radio frequency coil,
the single-resonance radio frequency coil is composed of a third equivalent capacitor (C3), a second equivalent capacitor (C2) and a second equivalent inductor (L2), an output port (6) is connected with one end of the third equivalent capacitor (C3), the third equivalent capacitor (C3) is respectively connected with one end of the second equivalent capacitor (C2) and one end of the second equivalent inductor (L2), the other end of the second equivalent capacitor (C2) and the other end of the second equivalent inductor (L2) are electrically connected,
the first equivalent inductance (L1) is the equivalent inductance of the balance capacitance module (3) and the resonance inductance module (4) which are connected in series,
the fourth equivalent capacitance (C4) is the equivalent capacitance of the input matching capacitance module (2),
the first equivalent capacitance (C1) is the equivalent capacitance of the output matching capacitance module (5),
the third equivalent inductor (L3) is the equivalent inductor of the first equivalent inductor (L1) and the fourth equivalent capacitor (C4) which are connected in series,
l3 is L2, C1 is C2, where L3 is the equivalent inductance of the third equivalent inductor (L3), L2 is the equivalent inductance of the second equivalent inductor (L2), C1 is the equivalent capacitance of the first equivalent capacitor (C1), and C2 is the equivalent capacitance of the second equivalent capacitor (C2).
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